The contribution MPEG SC29/WG11 M11611 (71st MPEG Meeting, Hong Kong, China, 17/21-01-2005) defines a method of streaming a digital item conforming to the concept defined by the MPEG-21 standard (ISO/IEC TR 2100-1:2004, Part 1: Vision, Technologies and Strategy) and represents the fundamental transaction and distribution unit in the MPEG-21 context. A digital item is an abstraction of one or more semantically linked multimedia contents (for example videos, images, audio) and any metadata linked to those contents, the whole constituting a transaction and end-use unit.
The metadata linked to the digital item is frequently written in the widely used data tree structuring language known as XML (eXtensible Mark-Up Language). Since the digital item is intended to be communicated, where applicable via Internet type networks, the problem arises of transmitting metadata contained therein, and more generally of transmitting XML documents.
In particular, it is beneficial to stream (transmit progressively) an XML document so that the destination entity can use the fragment it has received without having to wait to receive the entire document. Moreover, the use of an XML document is some times linked to the use of other data that is sent continuously, such as a video stream. It is then necessary to synchronize the various data streams mutually, and for this purpose to assign timing information to the fragments of the XML document.
The above-mentioned MPEG contribution proposes a solution for fragmenting a digital item and for assigning timing information to the fragments obtained. It applies to XML documents in particular, although it is not limited to them. That solution indicates the fragments to be transmitted by means of Xpath expressions, Xpath (XML Path Language, version 1.0, W3C Recommendation, 16 Nov. 1999) being an expression language for identifying a node or a set of nodes in an XML document. Moreover, a parameter is used to define a transmission time for those fragments.
That prior art processing method has some drawbacks, however:                Firstly, that method uses the expression language XPath to select the fragment of an XML document. The problem with XPath is that the entire XML document must be loaded into memory for an expression to be evaluated. For small XML documents, this is not a problem. In contrast, for large documents, that can consume considerable memory resources and can significantly reduce system performance.        Secondly, and for the same reason, the method cannot be employed for XML documents generated on the fly.        Thirdly, the timing information applied to a fragment cannot define a time relative to a preceding fragment.        